This invention relates generally to hot food serving appliances and, more particularly, to a counter top drop-in heating well which is more easily assembled than conventional wells heretofore available and wherein thermal cracking of the stainless steel well pan and heat stress failure of other components are substantially reduced or eliminated.
In the commercial food service industry, hot food serving appliances often utilize heating wells to store and keep bulk quantities of heated food warm until the food is served as individual portions. Typical of such units are those available from Seco Products, Southern Equipment Division, McGraw-Edison Company, Elgin, Illinois, the assignee of the present invention.
Other hot food serving units and food heating appliances are shown generally in the following U.S. Pat. Nos: 3,991,739--Hoffman; 3,443,063--Berger et. al.; 2,976,391--Carlson; 2,847,552--Gates; 2,709,215--Miller; 2,679,841--Muckler; 1,151,189--Kercher; and 1,120,758--Stirn.
Such hot food serving devices commonly include a heated, open-top well built into the counter top of a serving unit for heating a smaller pan that nests in the well from above and which holds the food. The well itself may include a larger deep-drawn pan, or container, in which the food pan nests as well as a high-temperature electric heating element for heating the well pan. The food pan is generally spaced from the walls of the well pan, and relatively low-temperature heat is transmitted from the well pan to the food pan to maintain the stored food at a warm temperature. Dry heating is accomplished by a combination of conduction, convection, and radiation while moist heating, such as by steam, can be accomplished by putting water in the heated well pan.
The well pan is typically formed from stainless steel for sanitary reasons, and the high-temperature heating element is secured to the underside of a heating plate positioned against the bottom of the well pan. Alternatively, the heating element may be located adjacent the bottom of the well pan without the use of a heating plate. In commercially available heating wells utilizing a heating plate, aluminum plates have heretofore been used. Aluminum, however, has a relatively high thermal conductivity factor, or K, typically 130 Btu/hr./ft./.degree.F. at 400.degree. Fahrenheit, and the high temperature of the electric heating element commonly used, typically in the order of 1100.degree. Fahrenheit, results in spot heating, or the rapid application of heat, through the aluminum plate to the portions of the well pan directly overlying the heating element. It has been found that cracking of the stainless steel well pan, from what metallurgists call carbide precipitation, may occur during continued use when the well pan is rapidly heated and then alternately heated and cooled at temperatures of approximately 800.degree. Fahrenheit or higher. Intergranular corrosion may result, leaving cracks in the stainless steel well pan which frequently occur in the area of the high-temperature heating element. Further, because the temperature of the heating element approaches the melting point of aluminum, some heating wells have incorporated supplementary thermostats for limiting the temperature which the heating element attains.
A problem also arises in providing means for securing the heating element in the well relative to the well pan. One manner of securing the high-temperature heating element against the well pan utilizes draw-down clamps secured to studs welded directly to the well pan. Alternatively, the heating element has also been bolted to the underside of the heating conducting plate which in turn, has been welded or otherwise mounted in the well unit. The studs and welds frequently break, however, because of the heat stress generated by the repeated expansion and contraction of these components during the use and non-use cycles of the heating well.
Finally, because the many component parts comprising the heating well unit in known hot food serving devices are assembled with bolts, sheet metal screws and/or by welding, such units are not only subject to heat stress failure but, in addition, are relatively expensive to fabricate, requiring complicated assembly procedures.